The goal of this series of studies is to determine the natural taxonomies that clinicians have of mental disorders and the cognitive consequences of having those taxonomies. The first series of studies (1a, 1b, 1c, and 1d) attempts to determine what are the "true" or "generic" mental disorder categories. The second series of studies investigates the organization of these generic mental disorder categories into hierarchies (2a) as well as the basic level (2b), the level of inductive privilege (2c), and essentialism and essentialist beliefs (3) within the hierarchies. Study 4 investigates the occurrence of these phenomena cross-culturally. All of the studies test whether these phenomena vary according to the profession of the participants (psychiatrists, psychologists and social workers), and level of expertise (students versus experts). Biological reductionism, by itself, will not explain psychopathology. Psychiatric classification must reflect how mental health professionals are influenced by cultural context (e.g., gender bias), economic factors (e.g., insurance reimbursement rates), and values (e.g., the subjectivity of humanism vs. objectivity of empirical science).